1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor device and a method for using the apparatus. More particularly, the present invention relates to a wafer stage including an electrostatic chuck, and to a method for dechucking a wafer using the wafer stage.
2. Description of the Related Art
Semiconductor devices are manufactured after performing many processes such as depositing a material layer on a wafer, patterning the deposited material layer, and removing unnecessary residuals on the wafer. To perform these processes repeatedly, a wafer is loaded on a wafer stage inside a chamber, the wafer is processed, and then unloaded.
In order to successively process a wafer, it is very important to chuck and fix the wafer in the chamber and to dechuck the wafer so that the wafer will not be damaged after processing. As semiconductor devices become highly integrated, the design rule becomes smaller, and the process margin becomes narrower. As a result, there is a greater need to chuck and fix the wafer without damaging the wafer during dechucking.
Methods for fixing the wafer to the wafer stage in the process chamber when the wafer is loaded on the wafer stage include using hardware structures such as clamps, using a vacuum to suction the rear side of the wafer (a vacuum chuck), using gravity, and using a piezoelectric effect. Various methods are available for dechucking the fixed wafer on the wafer stage after processing the wafer. The dechucking method used is chosen in accordance with the method used for fixing the wafer.
The most widely used method for fixing a wafer is the piezoelectric effect. In this method, an electrostatic chuck is used to fix the wafer, and the electrostatic chuck and a lifting means are used to dechuck the fixed wafer.
FIG. 1A illustrates a sectional view of a method for chucking a wafer using an electrostatic chuck according to the prior art. Referring to FIG. 1A, first, the structure of an electrostatic chuck 10 will be described, and then, a method for chucking a wafer 20 will be described. The electrostatic chuck 10 includes an upper insulating layer 2, an electrostatic electrode 4, a lower insulating layer 6, and a lower electrode 8. The lower electrode 8 controls the reaction speed of plasma when plasma is generated in the chamber (not shown). The electrostatic electrode 4 is connected to a DC generator (not shown), and positive charges or negative charges are distributed on the electrostatic electrode 4 by the DC generator. The electric charges on the electrostatic electrode 4 induce an electrostatic field such that the wafer 20 is chucked or dechucked. The electrostatic electrode 4 and the lower electrode 8 are insulated by the lower insulating layer 6, and the wafer 20 and the electrostatic electrode 4 are insulated by the upper insulating layer 2.
In a method for dechucking the wafer 20 according to the prior art, the wafer 20 is put on the electrostatic chuck 10, and an electrostatic field is induced by supplying power to the electrostatic electrode 4 under the upper insulating layer 2 on the upper surface of the electrostatic chuck 10. Positive charges accumulate on the electrostatic electrode 4 connected to the external DC generator (not shown), and negative charges accumulate on the lower surface of the wafer 20 by plasma generated on an upper portion of the wafer 20, thereby inducing an electrostatic field between the wafer 20 and the electrostatic electrode 4. When the upper surface of the electrostatic chuck 10 is completely in contact with the wafer 20, a clamping force is produced by the electrostatic field, and thus, the wafer 20 is chucked.
Meanwhile, some of the charges on the electrostatic electrode 4 of the electrostatic chuck 10 flow into the upper surface of the electrostatic chuck 10 through the upper insulating layer 2, and as time goes by, the electric charges accumulate. The clamping force between the wafer 20 and the electrostatic chuck 10 increases due to the accumulated electric charges. As a result, the magnitude of the clamping force grows larger than the voltage applied to the electrostatic electrode 4 of the electrostatic chuck 10. The wafer 20 and the electrostatic chuck 10 are stuck together by the increased clamping force when the wafer 20 and the electrostatic chuck 10 are dechucked.
FIG. 1B illustrates a sectional view of a method for dechucking a wafer 20 using an electrostatic chuck according to the prior art. When the wafer 20 is chucked, plasma formation on the upper portion of the wafer 20 stops, and the voltage supplied to the lower electrode 8 and the electrostatic electrode 4 of the electrostatic chuck 10 is turned off. As a result, the electric charges flow out and the clamping force is reduced. However, since a discharge time is necessary for the charges to flow when the clamping force is reduced, the wafer 20 becomes stuck to the electrostatic chuck 10.
When lift pins 12 are raised to dechuck a wafer 20 that is stuck to the electrostatic chuck 10, the force applied to the wafer 20 can easily damage the wafer 20. In order to prevent the sticking phenomenon, power is again supplied to the electrostatic electrode 4, in which positive charges remain, and negative charges flow into the electrostatic electrode 4. That is, electric charges having a charge opposite to those supplied to the electrostatic electrode 4 during chucking flow into the electrostatic electrode 4 during dechucking in order to neutralize the electrostatic electrode 4, thereby easily dechuck the wafer 20.
Subsequently, the lift pins 12 of the lifting means (not shown) are raised, and the wafer 20 is dechucked. However, in the method for supplying electric charges having an opposite polarity to the electrostatic electrode 4, the wafer 20 still possesses electric charges, and thus, the method is not of much help for dechucking.
In order to solve the aforementioned problems, it is a feature of an embodiment of the present invention to provide a wafer stage which is capable of easy dechucking and includes an electrostatic chuck which does not damage a wafer.
Another feature of an embodiment of the present invention is to provide a method for dechucking a wafer using the wafer stage.
In an effort to satisfy these and other features of the present invention, there is provided a wafer stage installed in a process chamber including: an electrostatic chuck support installed in a lower half of an enclosed chamber for supporting an electrostatic chuck; an electrostatic chuck installed on the electrostatic chuck support for chucking and supporting a wafer; a lifting means installed inside the electrostatic chuck and the electrostatic chuck support for lifting the wafer; and a grounding means including interconnections for connecting the lifting means to ground and a device for connecting the interconnections, which is installed between the interconnections, for allowing electric current flow and preventing electric current flow.
Preferably, the wafer stage further includes a guide ring installed around the electrostatic chuck for guiding the wafer when the wafer is chucked.
Preferably, the process chamber is a device for processing the wafer using plasma or a device for etching plasma.
Preferably, the lifting means includes: a plurality of lift pins for passing the electrostatic chuck and lifting the wafer; a lift pin support for supporting the lift pins in the electrostatic chuck support a connecting axis for connecting the lift pin support to a driving means; and a driving means for lifting the connecting axis. Also, it is preferable that the lift pins are formed of a conductive material and that the conductive material is aluminum.
Preferably, the electrostatic chuck includes: a lower electrode, which is connected to a DC generator located outside the enclosed chamber, for controlling the reaction speed of plasma; an insulating flat plate on an upper portion of the lower electrode; and an electrostatic electrode, which is connected to a RF generator outside the chamber, for generating static electricity. The electrostatic electrode may have a spiral form. The electrostatic chuck may further include a wafer cooler under the lower electrode in which cool water is circulated. The electrostatic electrode may include a plurality of electrostatic electrodes.
Preferably, the process chamber is a device for processing the wafer using plasma; more particularly, a device for etching plasma.
According to another embodiment of the present invention, there is provided a method for dechucking a wafer including: (a) processing a wafer formed on an electrostatic chuck of an enclosed chamber using plasma; (b) stopping plasma formation and turning off the voltage supplied to an electrostatic electrode and a lower electrode of the electrostatic chuck; (c) contacting a lifting means with a rear side of the wafer; (d) grounding the wafer; (e) neutralizing the electrostatic chuck by supplying power to the electrostatic electrode and neutralizing the wafer by supplying plasma to the wafer; and (f) dechucking the wafer by raising the lifting means. The electrostatic electrode may include a plurality of electrostatic electrodes.
Preferably, the processing in (a) is an etching process, and in (d), a device for connecting the interconnections of a grounding means connected to the lifting means is turned on.
Preferably, the plasma used in the chamber is generated on an upper electrode.
The present invention may prevent sparks between the wafer and the lifting means, and may cause the sticking phenomenon of the wafer to the electrostatic chuck to be overcome, thereby allowing easy dechucking of the wafer.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.